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For better soil, take time to fathom its components

SHARE For better soil, take time to fathom its components

At this time of year gardeners' thoughts often turn to the part of the garden that makes everything possible. Reflecting on the successes and failures of the year motivates one to look at basic growth factors, and soil is the basis of all successful gardening.

No garden ever produces the fruits of the soil unless limiting soil problems are corrected. No gardener should learn to live with such problems but should do everything possible to correct them.All soil has four basic components. An ideal soil is 25 percent air, 25 percent water, 45 percent mineral matter and 5 percent organic matter. Unfortunately, no one I know has ideal soil. Quality topsoil in Utah has less than 1 percent organic matter. To make matters worse, most Utah gardeners start with subsoil instead of top soil.

When analyzing garden soil, recognize what can be changed and what will, because of practical concerns, remain the same.

The air content of the soil is directly affected by the way the soil is handled. When it is tilled while it is too wet or when traffic compacts the soil, the air content is reduced. Reduced air content means no oxygen gets to the roots and so no respiration takes place. Without respiration there is no growth, so plants do poorly. Compaction is a serious problem with heavier soils.

The water fraction of the soil is also very important. Without the water, plants will not grow. Without enough air space in the soil, the water-holding capacity is greatly reduced. The fact that an ideal soil is 50 percent water and air should help us understand the critical need for keeping these components in balance.

The solid part of the soil is the other half. Most of this is mineral matter. The mineral portion is comprised of three particles: sand, silt and clay. Sand particles are the largest, clay particles the smallest and silt is intermediate between the other two. The relative amount of these three determines the soil texture. An ideal soil for most plants has approximately the same amounts of the three particles and is called a loam soil.

Sand particles are large and form open pore spaces. This creates both good aeration and good drainage. Clay particles are extremely small and hold the water and the nutrients well. Combining both would seemingly enhance the best characteristics of the particles and create a nearly ideal soil. Unfortunately, without the vital organic matter, clay particles sift between and fill up the spaces, creating low-grade cement.

Incorrect advice on amending soil often contains recommendations about adding sand to "lighten" the soil. The futility of this course of action is best illustrated because the top foot of soil on 10,000 square feet of land weighs 500,000 pounds. To amend the soil volume with one-third sand will require adding more than 160,000 pounds of sand on an average lot.

Since changing the soil texture or the relative amounts of sand, silt and clay particles is very difficult, look at other alternatives. Changing the soil structure is often the most successful and easiest alternative. Soil structure is defined as the aggregation of the soil particles or, in basic understandable terms, the formation of tiny dirt clods.

Aggregates are particles of soil that are clustered together into large particle sizes. Aggregate formation is affected by tillage, by freezing and thawing, by traffic and by the organic matter in the soil. The organic matter causes the soil aggregates to form because it contains many different substances that act as glue to stick the soil particles together. Among these are the waxes and lignins that form the nuclei of many aggregates. These start the process, and then the soil aggregates grow larger as more particles are attracted.

Relatively small amounts of organic matter will make a tremendous difference in the amount of aggregation in the soil. Organic matter improves the water-holding ability and the nutrient retention of sandy soils. It improves the drainage and the air content of clay soil and is the most beneficial material to add to any soil to improve the structure. Adding 1 percent organic matter makes more sense than adding 33 percent of an inorganic component such as sand.

Next week's article will cover vital information about finding organic matter and composting it so it will change the sticky mess in the garden into ideal, productive soil.